1. Field of the Invention
The present invention relates generally to the fields of molecular genetics and the biology of circadian rhythms. More specifically, the present invention relates to characterization and squencing of the mammalian circadian regulator m-rigui2.
2. Description of the Related Art
That genes control circadian rhythms of higher organisms was first established in the fruit fly by Konopka and Benzer (1971), who demonstrated that certain point mutations in Drosophila melanogaster caused altered circadian rhythms. The mutated gene, period (per), was subsequently isolated (Bargiello et al., 1984) and was found to be expressed in a circadian pattern (Hardin et al., 1990). This finding, and similar data from bacteria, fungi, and plants, has led to the general idea that periodically expressed genes constitute the physiological basis of circadian clocks in all living organisms (Hall and Rosbash, 1993; Takahashi, 1995; Dunlap, 1996).
The circadian rhythm which controls the mammalian sleep/wake cycle is being investigated intensively. However, the molecular components that constitute this circadian clock and the cellular organization that sets the phase and pace of the circadian clock in mammals were, until very recently, virtually unknown. Extensive physiological and behavioral studies have established that the circadian clock is characterized by a cycle of approximately 24 hours in duration, which, presumably, reflects the periodicity by which the Earth rotates. When organisms are placed in darkness or constant light, this clock is self-sustaining, behaving as a pacemaker. The endogenous clock is further distinguished by its ability to be entrained to a new light/dark regime by environmental cues such as light and temperature cycles (Pittendrigh, 1993; Takahashi, 1995). For example, pulses of light or exposure to different time zones reset the clock.
Some of the proteins that control the circadian process in mammals may be related to those found in fruit flies (Hall, 1990; Siwicki et al., 1992). In Drosophila, per and timeless (tim) encode essential components of the circadian clock (Sehgal et al., 1994; Reppert and Sauman, 1995). A heterodimer of Per and Tim proteins may regulate the circadian process by creating a negative feedback loop controlling per and tim expression (Zeng et al., 1996). Two lines of evidence: the oscillatory nature of per expression and the phenotype of per mutants, indicate the central role of the per gene in the circadian machinery of insects (Konopka and Benzer, 1971; Citri et al., 1987; Hardin et al., 1990; Hall, 1996).
The circadian clock mechanism can be divided into three components: (1) the input signaling mechanisms, (2) a circadian pacemaker or clock, and (3) the output signaling mechanisms. The input involves the transmission of diurnal environmental cues such as light to the clock, primarily through the retinohypothalamic tract (Moore, 1995). The circadian pacemaker integrates external cues and initiates a variety of signals to the output pathway. In other words, the output pathway transmits the clock's rhythm to the body to evoke a variety of circadian behaviors such as the sleep-wake cycle. Despite the complex role played by the circadian pacemaker, it may consist of a limited number of components. It may be possible to identify such components either through genetic screens in mice (King et al., 1997) or through homology screens of libraries (Tei et al., 1997).
The recent identification of a human ortholog of Drosophila per has created opportunities to investigate the mammalian circadian clock. This gene was independently discovered by Sun et al. (1997) who named it RIGUI (after an ancient Chinese sundial) and by Tei et al. (1997) who named it h-per (because of sequence similarity with Drosophila per). The mouse homolog, m-rigui/m-per, is the first mammalian gene that meets the properties of a circadian regulator, such as circadian expression in the suprachiasmatic nucleus (SCN), self-sustained oscillation, and entrainment of circadian expression by external light cues. M-rigui1 and m-rigui2 are also known in the art as mPer1 and mPer2. Recently, a third homolog, known as mPer3, has been identified and characterized (Zylka, et al. 1998, Takumi et al, 1998)
The prior art is deficient in the lack of the characterization and squencing of the mammalian circadian regulator m-rigui2. The present invention fulfills this longstanding need and desire in the art.